1. Field of the Invention
The invention relates to a catalyst protection device and catalyst protection method for an internal combustion engine.
2. Description of Related Art
Some internal combustion engines (engines) include an exhaust purification catalyst (hereinafter, simply referred to as catalyst where appropriate) for purifying exhaust gas. However, when the catalyst is excessively heated by high-temperature exhaust gas, or the like, the purification capacity of the catalyst may decrease. In order to keep the high purification capacity of the catalyst, a technique for cooling the catalyst by decreasing the temperature of exhaust gas with the use of the heat of vaporization of fuel through an increase in fuel injection amount, may be used. The increase in the amount of injected fuel in this case is termed over-temperature protection (OT) increase. The amount of injected fuel that is increased through the OT increase is termed OT increase value.
Japanese Patent Application Publication No. 10-205375 (JP 10-205375 A) describes a fuel supply control system in which, when a high-load operating state of an internal combustion engine is detected and an estimated temperature of an exhaust control device is higher than or equal to a predetermined temperature, the amount of fuel that is supplied to the internal combustion engine is increased.
Incidentally, the distribution of temperature in the catalyst included in the exhaust control device varies in an exhaust gas flow direction. In addition, it is presumable that a temperature state at the upstream side of the catalyst in the exhaust gas flow direction propagates to the downstream side of the catalyst in the exhaust gas flow direction. However, in JP 10-205375 A, such a temperature distribution in the exhaust gas flow direction in the catalyst is not considered. As a result, the exhaust control device may partially enter an excessive-temperature state.